1. Technical Field
This invention relates to a method and apparatus for modifying surfaces of metal parts by means of high-density energy and build-up welding.
2. Background Art
The parts of aluminum castings that are subject partially to a large thermal and/or mechanical load, such as cylinder heads of internal combustion engines, require modification of their surfaces (reinforcement of surfaces). To satisfy such requirement there have been recently proposed different methods of surface remelting treatment or alloy remelting treatment (addition of heat-resistant elements) by means of high-density energy irradiation such as irradiation of laser beams, electron beams, tungusten inert-gas (TIG) arcs, or metal inert-gas (MIG) arcs.
Features of these proposed methods, which relate to the high-density energy to be used, include capability of deepening the alloyed layer (by laser and electron beams). direct alloying of the casting surface (by laser and electron beams, and TIG arcs) and high speed welding.
However, these methods of high-density energy irradiation have such disadvantages as high price of equipment (laser beams), long treatment time, necessity of in-vacuum treatment (electron beams) and the deleterious effect of porocity defects of the base metal which is liable to cause blow holes (TIG and MIG arcs).
In consideration of the above-mentioned disadvantages it is desired to use, as a method of surface modification of low cost and high productivity, alloying of base metals (build-up welding) by TIG arc welding or MIG arc welding. However, these methods involve also the problem that the quantity of alloying elements which can be added to the base metal surface layer is limited to a low level (TIG arc welding), and that the casting surface cannot be subjected to direct alloy welding but requires preliminary machining (MIG welding).